Process for producing blends of syndiotactic 1, 2-polybutadiene and rubbery elastomers with an iron-based catalyst system

ABSTRACT

Blends of syndiotactic 1,2-polybutadiene and rubbery elastomers are prepared by a process that comprises polymerizing 1,3-butadiene monomer into syndiotactic 1,2-polybutadiene within a rubber cement of at least one rubbery elastomer by using an iron-based catalyst composition that is formed by combining an iron-containing compound, a hydrogen phosphite, and an organoaluminum compound.

FIELD OF THE INVENTION

The present invention is directed toward a process for producing blendsof syndiotactic 1,2-polybutadiene and rubbery elastomers. Moreparticularly, the process of this invention comprises polymerizing1,3-butadiene into syndiotactic 1,2-polybutadiene within a rubber cementby using an iron-based catalyst composition that is formed by combiningan iron-containing compound, a hydrogen phosphite, and an organoaluminumcompound.

BACKGROUND OF THE INVENTION

Syndiotactic 1,2-polybutadiene is a crystalline thermoplastic resin thathas a stereoregular structure in which the side-chain vinyl groups arelocated alternately on the opposite sides in relation to the polymericmain chain. Syndiotactic 1,2-polybutadiene is a unique material thatexhibits the properties of both plastics and rubber, and therefore ithas many uses. For example, films, fibers, and various molded articlescan be made by utilizing syndiotactic 1,2-polybutadiene. It can also beblended into and co-cured with natural and synthetic rubbers.

Syndiotactic 1,2-polybutadiene can be made by solution, emulsion, orsuspension polymerization. Generally, syndiotactic 1,2-polybutadiene hasa melting temperature within the range of about 195° C. to about 215°C., but due to processability considerations, it is generally desirablefor syndiotactic 1,2-polybutadiene to have a melting temperature of lessthan about 195° C.

Because syndiotactic 1,2-polybutadiene is insoluble in common solventsat normal polymerization temperatures, a common technical difficulty inthe synthesis of syndiotactic 1,2-polybutadiene is that thepolymerization mixture is an extremely thick slurry at the commerciallydesirable polymer concentration of 10% to 25% by weight. This thickslurry becomes difficult to stir and transfer, thereby diminishing heattransfer efficiency and interfering with proper process control. Also,the slurry contributes to reactor fouling due to the undesirablebuild-up of insoluble polymer on the baffles, agitator blades, agitatorshafts, and walls of the polymerization reactor. It is thereforenecessary to clean the reactor on a regular basis, which results infrequent shutdowns of continuous processes and serious limitations ofthe run length of batch processes. The task of cleaning the fouledreactor is generally difficult and time-consuming. All of thesedrawbacks detrimentally affect productivity and the cost of operation.It would be advantageous to develop a method of synthesizingsyndiotactic 1,2-polybutadiene that avoids this frequent reactor foulingproblem.

Various transition metal catalyst systems based on cobalt, titanium,vanadium, chromium, and molybdenum for the preparation of syndiotactic1,2-polybutadiene have been reported. The majority of these catalystsystems, however, have no practical utility because they have lowcatalytic activity or poor stereoselectivity, and in some cases theyproduce low molecular weight polymers or partially crosslinked polymersunsuitable for commercial use.

The following two cobalt-based catalyst systems are well known for thepreparation of syndiotactic 1,2-polybutadiene on a commercial scale: (1)a catalyst system containing cobalt bis(acetylacetonate),triethylaluminum, water, and triphenylphosphine (U.S. Pat. Nos.3,498,963 and 4,182,813), and (2) a catalyst system containing cobalttris(acetylacetonate), triethylaluminum, and carbon disulfide (U.S. Pat.No. 3,778,424). These cobalt-based catalyst systems also have seriousdisadvantages.

The first cobalt catalyst system referenced above yields syndiotactic1,2-polybutadiene having very low crystallinity. Also, this catalystsystem develops sufficient catalytic activity only when halogenatedhydrocarbon solvents are used as the polymerization medium, andhalogenated solvents present toxicity problems.

The second cobalt catalyst system referenced above uses carbon disulfideas one of the catalyst components. Because of its low flash point,obnoxious smell, high volatility, and toxicity, carbon disulfide isdifficult and dangerous to use, and requires expensive safety measuresto prevent even minimal amounts escaping into the atmosphere.Furthermore, the syndiotactic 1,2-polybutadiene produced with thiscobalt catalyst system has a very high melting temperature of about200-210° C., which makes it difficult to process the polymer. Althoughthe melting temperature of the syndiotactic 1,2-polybutadiene producedwith this cobalt catalyst system can be reduced by employing a catalystmodifier as a fourth catalyst component, the presence of this catalystmodifier has adverse effects on the catalyst activity and polymeryields. Accordingly, many restrictions are required for the industrialutilization of these cobalt-based catalyst systems.

It is well known that the physical properties of rubbery elastomers canbe improved by blending crystalline polymers therein. For example,incorporating syndiotactic 1,2-polybutadiene into rubber compositionsthat are utilized in the supporting carcass of tires greatly improvesthe green strength of those compositions. Also, incorporatingsyndiotactic 1,2-polybutadiene into tire tread compositions can reducethe heat build-up and improve the wear characteristics of tires. Thegreen strength of synthetic rubbers such as cis-1,4-polybutadiene canalso be improved by incorporating a small amount of syndiotactic1,2-polybutadiene.

Blends of crystalline polymers and rubbery elastomers are typicallyprepared by standard mixing techniques. For example, these blends can beprepared by mixing or kneading and heat-treating a crystalline polymerand a rubbery elastomer by utilizing generally known mixing equipmentsuch as a Banbury mixer, a Brabender mixer, an extruder, a kneader, or amill mixer. These high-temperature mixing procedures, however, havecertain drawbacks including high processing costs, polymer degradationand crosslinking, inadequate mixing, as well as various processlimitations. Due to the high vinyl content of syndiotactic1,2-polybutadiene, polymer degradation and crosslinking is aparticularly severe problem for mixing syndiotactic 1,2-polybutadienewith elastomers at high temperatures.

Attempts to polymerize 1,3-butadiene into syndiotactic 1,2-polybutadienewithin a rubber cement have been hampered by the same catalystinefficiencies and toxicities mentioned above. For example, U.S. Pat.No. 4,379,889 teaches polymerizing 1,3-butadiene into syndiotactic1,2-polybutadiene within a rubber cement by using a catalyst systemcomprising a cobalt compound, a dialkylaluminum halide, carbondisulfide, and an electron donative compound. And, U.S. Pat. No.5,283,294 teaches a similar process that employs a catalyst systemcomprising a cobalt compound, an organoaluminum compound, and carbondisulfide. These methods, however, are inferior because the catalystsystems that are employed suffer from the foregoing disadvantages.

Therefore, it would be advantageous to develop a new and significantlyimproved process for producing blends of syndiotactic 1,2-polybutadieneand rubbery elastomers.

SUMMARY OF THE INVENTION

In general, the present invention provides a process for preparingblends of syndiotactic 1,2-polybutadiene and rubbery elastomerscomprising the steps of (1) providing a mixture of a rubber cement and1,3-butadiene monomer, and (2) polymerizing the 1,3-butadiene monomerinto syndiotactic 1,2-polybutadiene within the rubber cement by using acatalyst composition that is the combination of or the reaction productof ingredients comprising an iron-containing compound, a hydrogenphosphite, and an organoaluminum compound.

The present invention further provides a process for producing blends ofsyndiotactic 1,2-polybutadiene and rubbery elastomers comprising thesteps of (1) providing a mixture of a rubber cement and 1,3-butadienemonomer, and (2) polymerizing the 1,3-butadiene monomer intosyndiotactic 1,2-polybutadiene within the rubber cement by using acatalyst composition that is formed by combining an iron-containingcompound, a hydrogen phosphite, and an organoaluminum compound.

The present invention also provides a blend of syndiotactic1,2-polybutadiene and rubbery elastomers prepared by a processcomprising the steps of (1) providing a mixture of a rubber cement and1,3-butadiene monomer, and (2) polymerizing the 1,3-butadiene monomerinto syndiotactic 1,2-polybutadiene within the rubber cement by using acatalyst composition that is the combination of or the reaction productof ingredients comprising an iron-containing compound, a hydrogenphosphite, and an organoaluminum compound.

Advantageously, the process of this invention directly provides blendsof syndiotactic 1,2-polybutadiene and rubbery elastomers by synthesizingsyndiotactic 1,2-polybutadiene within a rubbery cement and therebyobviates the need for high-temperature mixing. Also, good dispersion ofsyndiotactic 1,2-polybutadiene throughout rubbery elastomers can beeasily and economically achieved. Significantly, the process of thisinvention eliminates the problems of high processing costs, polymerdegradation and crosslinking, inadequate mixing, and various processlimitations that are associated with high-temperature mixing procedures.The process of this invention also alleviates the problems of rubbercement thickness and reactor fouling that are associated with thesynthesis of syndiotactic 1,2-polybutadiene in the absence of a rubberyelastomer.

In addition, the iron-based catalyst system employed in this inventionhas very high catalytic activity and stereoselectivity for thesyndiospecific polymerization of 1,3-butadiene. This activity andselectivity, among other advantages, allows syndiotactic1,2-polybutadiene to be produced in very high yields within a rubbercement. Moreover, this iron-based catalyst composition is very versatileand capable of producing syndiotactic 1,2-polybutadiene with a widerange of melting temperatures without the need for a catalyst modifierthat may have adverse effects on the catalyst activity and polymeryields. Additionally, this catalyst composition does not contain carbondisulfide, and therefore the toxicity, objectionable smell, dangers, andexpense associated with the use of carbon disulfide are eliminated.Further, this catalyst composition is iron-based, and iron compounds aregenerally stable, inexpensive, relatively innocuous, and readilyavailable. Furthermore, this catalyst composition has high catalyticactivity in a wide variety of solvents including theenvironmentally-preferred nonhalogenated solvents such as aliphatic andcycloaliphatic hydrocarbons.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is generally directed toward a process forproducing blends of syndiotactic 1,2-polybutadiene and rubberyelastomers. It has now been found that blends of syndiotactic1,2-polybutadiene and rubbery elastomers can be directly produced bypolymerizing 1,3-butadiene monomer into syndiotactic 1,2-polybutadienewithin a rubbery cement by using an iron-based catalyst composition.

According to the process of the present invention, blends ofsyndiotactic 1,2-polybutadiene and rubbery elastomers are produced bythe steps of: (1) providing a mixture of a rubber cement and1,3-butadiene monomer, where the rubber cement includes at least onerubbery elastomer within an organic solvent, and (2) polymerizing the1,3-butadiene monomer into syndiotactic 1,2-polybutadiene within therubber cement by using an iron-based catalyst composition. Theiron-based catalyst composition employed to synthesize the syndiotactic1,2-polybutadiene comprises (a) an iron-containing compound, (b) ahydrogen phosphite, and (c) an organoaluminum compound.

Although the preferred embodiment of the present invention is directedtoward the polymerization of 1,3-butadiene into syndiotactic1,2-polybutadiene within a rubber cement, other conjugated dienemonomers can be polymerized by using the iron-based catalyst compositionto form conjugated diene polymers, preferably crystalline polymers,within a rubber cement.

The rubber cement employed in this invention is a solution, preferablyviscous, of at least one rubbery elastomer in an organic solvent.Virtually any type of rubbery elastomer can be used to prepare therubber cement. Some specific examples of suitable rubbery elastomersinclude, but are not limited to, natural rubber, cis-1,4-polybutadiene,amorphous 1,2-polybutadiene, polyisoprene, polyisobutylene, neoprene,ethylene-propylene copolymer rubber (EPR), styrene-butadiene rubber(SBR), styrene-isoprene rubber (SIR), styrene-isoprene-butadiene rubber(SIBR), styrene-butadiene-styrene block copolymer (SBS),styrene-butadiene block copolymer (SB), hydrogenatedstyrene-butadiene-styrene block copolymer (SEBS), hydrogenatedstyrene-butadiene block copolymer (SEB), styrene-isoprene-styrene blockcopolymer (SIS), styrene-isoprene block copolymer (SI), hydrogenatedstyrene-isoprene-styrene block copolymer (SEPS), hydrogenatedstyrene-isoprene block copolymer (SEP), polysulfide rubber, acrylicrubber, urethane rubber, silicone rubber, epichlorohydrin rubber, andthe like. Mixtures of the above rubbery elastomers may also be used.These rubbery elastomers are well known and, for the most part, arecommercially available. Also, those skilled in the art will be able toreadily synthesize these rubbery elastomers by using techniques that arewell known in the art.

The rubber cement can be prepared by dissolving the above-mentionedrubbery elastomers in an organic solvent. When commercially availablerubbery elastomers are employed to prepare the rubber cement, it may benecessary to purify the commercial products before use in order toremove residual water and additives that may become catalyst poisons inthe subsequent step of polymerizing 1,3-butadiene monomer intosyndiotactic 1,2-polybutadiene within the rubber cement.

In a preferred embodiment, the rubber cement is prepared in situ bypolymerizing one or more appropriate monomers into rubbery elastomers inan organic solvent within the same reactor that is subsequently used forpolymerizing 1,3-butadiene into syndiotactic 1,2-polybutadiene. As notedabove, many methods of synthesizing the above-mentioned rubberyelastomers are well known in the art. Preferably, however, the catalystutilized in preparing the rubbery elastomers should not contain anyingredients that may become a catalyst poison in the subsequent step ofpolymerizing 1,3-butadiene monomer into syndiotactic 1,2-polybutadienewithin the rubber cement.

Coordination catalyst systems, which are well known in the art, can beused for preparing the rubber cement of rubbery elastomers in situ. Forexample, lanthanide-based catalyst systems comprising a lanthanidecompound such as a neodymium compound, an alkylating agent, and a sourceof halogen are described in U.S. Pat. Nos. 3,297,667, 3,541,063,3,794,604, which are incorporated herein by reference. Theselanthanide-based catalyst systems are particularly useful forpolymerizing 1,3-butadiene monomer into cis-1,4-polybutadiene rubber.When a coordination catalyst such as the lanthanide-based system is usedto synthesize rubbery elastomers, the catalyst is preferably inactivatedby adding a terminator prior to proceeding with the synthesis ofsyndiotactic 1,2-polybutadiene within the rubber cement. Suitableterminators include, but are not limited to, alcohols, carboxylic acids,inorganic acids, water, and mixtures thereof. It is not alwaysnecessary, however, to add a terminator to inactivate the catalystsystem used to synthesize the rubbery elastomers since it is believedthat the catalyst may be inactivated by the hydrogen phosphite componentof the iron-based catalyst composition that is subsequently used tosynthesize the syndiotactic 1,2-polybutadiene. This has been found to betrue in the case where a coordination catalyst that includes a neodymiumcompound, an alkylating agent, and a source of halogen ion is used tosynthesize the rubbery elastomers.

Also, anionic polymerization initiators, which are well known in theart, can be used for preparing the rubber cement of rubbery elastomersin situ. These initiators include, but are not limited to, organolithiuminitiators such as butyllithium or functional initiators such as lithiumamide initiators, aminoalkyl lithium initiators, and organotin lithiuminitiators. Exemplary initiators are described in U.S. Pat. Nos.5,153,159, 5,268,439, 5,274,106, 5,238,893, 5,332,810, 5,329,005,5,578,542, 5,393,721, 5,491,230, 5,521,309, 5,496,940, 5,574,109,5,523,364,5,527,753, and 5,550,203. These initiators are particularlyuseful for synthesizing conjugated diene elastomers or copolymers ofconjugated diene monomers and vinyl-substituted aromatic monomers. Whenan anionic initiator is used to prepare the rubbery elastomers, it ispreferred to quench the polymerization by adding a terminator prior toproceeding with the synthesis of syndiotactic 1,2-polybutadiene withinthe rubber cement. Suitable terminators include, but are not limited to,metal halides, organic halides, alcohols, carboxylic acids, inorganicacids, sulfonic acid, water, and mixtures thereof. Metal halides, suchas diethylaluminum chloride and ethylaluminum dichloride, are preferred,as are organic halides such as trimethylsilylchloride. Failure to quenchthe anionic polymerization may interfere with the formation ofsyndiotactic 1,2-polybutadiene.

Other methods that are useful for synthesizing rubbery elastomers areknown in the art, and the practice of this invention should not belimited to the selection of any particular elastomer, or to anyparticular method for synthesizing rubbery elastomers.

Suitable monomers that can be polymerized to form the rubbery elastomersinclude conjugated diene monomers. Vinyl-substituted aromatic monomerscan be copolymerized with one or more conjugated diene monomers to formrubbery elastomers. Some specific examples of suitable conjugated dienemonomers that can be polymerized into rubbery elastomers include1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene,isoprene, 1,3-pentadiene, 2-methyl-1,3-pentadiene,2,3-dimethyl-1,3-pentadiene, and 4,5-diethyl-1,3-octadiene. Somespecific examples of suitable vinyl-substituted aromatic monomers thatcan be polymerized into rubbery elastomers include styrene,4-methylstyrene, α-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene,2,4,6-trimethylstyrene, 4-dodecylstyrene, 2,3,4,5-tetraethylstyrene,3-methyl-5-normal-hexylstyrene, 4-phenylstyrene,2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 1-vinylnaphthalene,3-ethyl-1-vinylnaphthalene, 6-isopropyl-1-vinylnaphthalene,6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnaphthalene, and thelike, and mixtures thereof.

In preparing the rubber cement, it is normally desirable to select anorganic solvent that is inert with respect to the catalyst systems thatwill be employed to synthesize the rubbery elastomers and thesyndiotactic 1,2-polybutadiene. Suitable types of organic solvents thatcan be utilized in preparing the rubber cement include, but are notlimited to, aliphatic, cycloaliphatic, and aromatic hydrocarbons. Somerepresentative examples of suitable aliphatic solvents includen-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane,isopentane, isohexanes, isoheptanes, isooctanes, 2,2-dimethylbutane,petroleum ether, kerosene, petroleum spirits, and the like. Somerepresentative examples of suitable cycloaliphatic solvents includecyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, andthe like. Some representative examples of suitable aromatic solventsinclude benzene, toluene, xylenes, ethylbenzene, diethylbenzene,mesitylene, and the like. Commercial mixtures of the above hydrocarbonsmay also be used. For environmental reasons, aliphatic andcycloaliphatic solvents are highly preferred.

The concentration of the rubbery elastomers in the rubber cement variesdepending on the types of the rubbery elastomers and organic solventemployed. It is generally preferred that the concentration of therubbery elastomers be in a range of from about 5% to about 35% by weightof the rubber cement, more preferably from about 10% to 30% by weight ofthe rubber cement, and even more preferably from about 15% to about 25%by weight of the rubber cement.

The foregoing rubber cement is then utilized as a polymerization mediumfor the stereospecific polymerization of 1,3-butadiene monomer intosyndiotactic 1,2-polybutadiene. Thus, 1,3-butadiene monomer, aniron-based catalyst composition, and optionally additional organicsolvent are added to the rubber cement. The order in which the1,3-butadiene monomer, iron-based catalyst composition, and the solventare added to the rubber cement does not limit the scope of theinvention, although it may be preferable to add the iron-based catalystcomposition, or at least an ingredient thereof, prior to the addition ofthe 1,3-butadiene monomer.

The amount of 1,3-butadiene monomer added to the rubber cement iscontingent upon the proportion of syndiotactic 1,2-polybutadiene desiredin the resultant polymer blend. The additional organic solvent can beselected from the group of the organic solvents mentioned above for thepreparation of the rubber cement, and may be the same as or differentfrom the organic solvent used in preparing the rubber cement. It shouldbe noted that the addition of 1,3-butadiene monomer to the rubber cementmay not be required in the case where 1,3-butadiene monomer is employedto prepare the rubbery elastomers and the polymerization is stoppedbefore all the 1,3-butadiene is consumed, thereby providing theremaining 1,3-butadiene monomer for synthesizing the syndiotactic1,2-polybutadiene without the need to add additional 1,3-butadienemonomer.

The polymerization of 1,3-butadiene into syndiotactic 1,2-polybutadienewithin the rubber cement is catalyzed by an iron-based catalystcomposition that is described in co-pending patent applications U.S.Ser. No. 09/1 72,305, U.S. Ser. Nos. 09/173,956, and Ser. No.09/439,861, which are incorporated in their entirety herein byreference. Generally, these catalyst compositions are formed bycombining (a) an iron-containing compound, (b) a hydrogen phosphite, and(c) an organoaluminum compound. In addition to the three catalystingredients (a), (b), and (c), other organometallic compounds or Lewisbases that are known in the art can also be added, if desired.

Various iron-containing compounds or mixtures thereof can be employed asingredient (a) of the iron-based catalyst composition utilized in thisinvention. It is generally advantageous to employ iron-containingcompounds that are soluble in a hydrocarbon solvent such as aromatichydrocarbons, aliphatic hydrocarbons, or cycloaliphatic hydrocarbons.Hydrocarbon-insoluble iron-containing compounds, however, can besuspended in the polymerization medium to form the catalytically activespecies, and are therefore also useful.

The iron atom in the iron-containing compounds can be in variousoxidation states including, but not limited to, the 0, +2, +3, and +4oxidation states. It is preferable to use divalent iron compounds (alsocalled ferrous compounds), wherein the iron is in the +2 oxidationstate, and trivalent iron compounds (also called ferric compounds),wherein the iron is in the +3 oxidation state. Suitable types ofiron-containing compounds that can be utilized in this inventioninclude, but are not limited to, iron carboxylates, iron carbamates,iron dithiocarbamates, iron xanthates, iron β-diketonates, ironalkoxides, iron aryloxides, and organoiron compounds.

Some specific examples of suitable iron carboxylates include iron(II)formate, iron(III) formate, iron(II) acetate, iron(III) acetate,iron(II) acrylate, iron(III) acrylate, iron(II) methacrylate, iron(III)methacrylate, iron(II) valerate, iron(III) valerate, iron(II) gluconate,iron(III) gluconate, iron(II) citrate, iron(III) citrate, iron(II)fumarate, iron(III) fumarate, iron(II) lactate, iron(III) lactate,iron(II) maleate, iron(III) maleate, iron(II) oxalate, iron(III)oxalate, iron(II) 2-ethylhexanoate, iron(III) 2-ethylhexanoate, iron(II)neodecanoate, iron(III) neodecanoate, iron(II) naphthenate, iron(III)naphthenate, iron(II) stearate, iron(III) stearate, iron(II) oleate,iron(III) oleate, iron(II) benzoate, iron(III) benzoate, iron(II)picolinate, and iron(III) picolinate.

Some specific examples of suitable iron carbamates include iron(II)dimethylcarbamate, iron(III) dimethylcarbamate, iron(II)diethylcarbamate, iron(III) diethylcarbamate, iron(II)diisopropylcarbamate, iron(III) diisopropylcarbamate, iron(II)dibutylcarbamate, iron(III) dibutylcarbamate, iron(II)dibenzylcarbamate, and iron(III) dibenzylcarbamate.

Some specific examples of suitable iron dithiocarbamates includeiron(II) dimethyldithiocarbamate, iron(III) dimethyldithiocarbamate,iron(II) diethyldithiocarbamate, iron(III) diethyldithiocarbamate,iron(II) diisopropyldithiocarbamate, iron(III)diisopropyldithiocarbamate, iron(II) dibutyldithiocarbamate, iron(III)dibutyldithiocarbamate, iron(II) dibenzyldithiocarbamate, and iron(III)dibenzyldithiocarbamate.

Some specific examples of suitable iron xanthates include iron(II)methylxanthate, iron(III) methylxanthate, iron(II) ethylxanthate,iron(III) ethylxanthate, iron(II) isopropylxanthate, iron(III)isopropylxanthate, iron(II) butylxanthate, iron(III) butylxanthate,iron(II) benzylxanthate, and iron(III) benzylxanthate.

Some specific examples of suitable iron β-diketonates include iron(II)acetylacetonate, iron(III) acetylacetonate, iron(II)trifluoroacetylacetonate, iron(III) trifluoroacetylacetonate, iron(II)hexafluoroacetylacetonate, iron(III) hexafluoroacetylacetonate, iron(II)benzoylacetonate, iron(III) benzoylacetonate, iron(II)2,2,6,6-tetramethyl-3,5-heptanedionate, and iron(III)2,2,6,6-tetramethyl-3,5-heptanedionate.

Some specific examples of suitable iron alkoxides or aryloxides includeiron(II) methoxide, iron(III) methoxide, iron(II) ethoxide, iron(III)ethoxide, iron(II) isopropoxide, iron(III) isopropoxide, iron(II)2-ethylhexoxide, iron(III) 2-ethylhexoxide, iron(II) phenoxide,iron(III) phenoxide, iron(II) nonylphenoxide, iron(III) nonylphenoxide,iron(II) naphthoxide, and iron(III) naphthoxide.

The term “organoiron compound” refers to any iron compound containing atleast one iron-carbon bond. Some specific examples of suitableorganoiron compounds include bis(cyclopentadienyl)iron(II) (also calledferrocene), bis(pentamethylcyclopentadienyl) iron(II) (also calleddecamethylferrocene), bis(pentadienyl) iron(II),bis(2,4-dimethylpentadienyl) iron(II), bis(allyl) dicarbonyliron(II),(cyclopentadienyl)(pentadienyl) iron(II), tetra(1-norbornyl) iron(IV),(trimethylenemethane)tricarbonyliron(II), bis(butadiene)carbonyliron(0),butadienetricarbonyliron(0), and bis(cyclooctatetraene)iron(0).

Useful hydrogen phosphite compounds that can be employed as ingredient(b) of the iron-based catalyst composition utilized in this inventionare either acyclic hydrogen phosphites, cyclic hydrogen phosphites, ormixtures thereof.

In general, the acyclic hydrogen phosphites may be represented by thefollowing keto-enol tautomeric structures:

where R¹ and R², which may be the same or different, are mono-valentorganic groups. Preferably, R¹ and R² are hydrocarbyl groups such as,but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl,cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl,aralkyl, alkaryl, and alkynyl groups, with each group preferablycontaining from 1 carbon atom, or the appropriate minimum number ofcarbon atoms to form the group, up to 20 carbon atoms. These hydrocarbylgroups may contain heteroatoms such as, but not limited to, nitrogen,oxygen, silicon, sulfur, and phosphorus atoms. The acyclic hydrogenphosphites exist mainly as the keto tautomer (shown on the left), withthe enol tautomer (shown on the right) being the minor species. Theequilibrium constant for the above-mentioned tautomeric equilibrium isdependent upon factors such as the temperature, the types of R¹ and R²groups, the type of solvent, and the like. Both tautomers may beassociated in dimeric, trimeric or oligomeric forms by hydrogen bonding.Either of the two tautomers or mixtures thereof can be employed as theingredient (b) of the catalyst composition of this invention.

Some representative and non-limiting examples of suitable acyclichydrogen phosphites are dimethyl hydrogen phosphite, diethyl hydrogenphosphite, dibutyl hydrogen phosphite, dihexyl hydrogen phosphite,dioctyl hydrogen phosphite, didecyl hydrogen phosphite, didodecylhydrogen phosphite, dioctadecyl hydrogen phosphite,bis(2,2,2-trifluoroethyl) hydrogen phosphite, diisopropyl hydrogenphosphite, bis(3,3-dimethyl-2-butyl) hydrogen phosphite,bis(2,4-dimethyl-3-pentyl) hydrogen phosphite, di-t-butyl hydrogenphosphite, bis(2-ethylhexyl) hydrogen phosphite, dineopentyl hydrogenphosphite, bis(cyclopropylmethyl) hydrogen phosphite, bis(cyclobutylmethyl) hydrogen phosphite, bis(cyclopentylmethyl) hydrogenphosphite, bis(cyclohexylmethyl) hydrogen phosphite, dicyclobutylhydrogen phosphite, dicyclopentyl hydrogen phosphite, dicyclohexylhydrogen phosphite, dimethyl hydrogen phosphite, diphenyl hydrogenphosphite, dinaphthyl hydrogen phosphite, dibenzyl hydrogen phosphite,bis(1-naphthylmethyl) hydrogen phosphite, diallyl hydrogen phosphite,dimethallyl hydrogen phosphite, dicrotyl hydrogen phosphite, ethyl butylhydrogen phosphite, methyl hexyl hydrogen phosphite, methyl neopentylhydrogen phosphite, methyl phenyl hydrogen phosphite, methyl cyclohexylhydrogen phosphite, methyl benzyl hydrogen phosphite, and the like.Mixtures of the above dihydrocarbyl hydrogen phosphites may also beutilized.

In general, cyclic hydrogen phosphites contain a divalent organic groupthat bridges between the two oxygen atoms that are singly-bonded to thephosphorus atoms. These cyclic hydrogen phosphites may be represented bythe following keto-enol tautomeric structures:

where R³ is a divalent organic group. Preferably, R³ is a hydrocarbylenegroup such as, but not limited to, alkylene, cycloalkylene, substitutedalkylene, substituted cycloalkylene, alkenylene, cycloalkenylene,substituted alkenylene, substituted cycloalkenylene, arylene, andsubstituted arylene groups, with each group preferably containing from 1carbon atom, or the appropriate minimum number of carbon atoms to formthe group, up to 20 carbon atoms. These hydrocarbylene groups maycontain heteroatoms such as, but not limited to, nitrogen, oxygen,silicon, sulfur, and phosphorus atoms. The cyclic hydrogen phosphitesexist mainly as the keto tautomer (shown on the left), with the enoltautomer (shown on the right) being the minor species. The equilibriumconstant for the above-mentioned tautomeric equilibrium is dependentupon factors such as the temperature, the types of R³ group, the type ofsolvent, and the like. Both tautomers may be associated in dimeric,trimeric or oligomeric forms by hydrogen bonding. Either of the twotautomers or mixtures thereof can be employed as the ingredient (b) ofthe catalyst composition of this invention.

The cyclic hydrogen phosphites may be synthesized by thetransesterification reaction of an acyclic dihydrocarbyl hydrogenphosphite (usually dimethyl hydrogen phosphite or diethyl hydrogenphosphite) with an alkylene diol or an arylene diol. Procedures for thistransesterification reaction are well known to those skilled in the art.Typically, the transesterification reaction is carried out by heating amixture of an acyclic dihydrocarbyl hydrogen phosphite and an alkylenediol or an arylene diol. Subsequent distillation of the side-productalcohol (usually methanol or ethanol) that results from thetransesterification reaction leaves the new-made cyclic hydrogenphosphite.

Some specific examples of suitable cyclic alkylene hydrogen phosphitesare 2-oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5,5-dimethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-methyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5-ethyl-5-methyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5,5-diethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5-methyl-5-propyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-isopropyl-5,5-dimethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4,6-dimethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-propyl-5-ethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-methyl-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-dimethyl-1,3,2-dioxaphospholane,2-oxo-(2H)-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane, and the like.Mixtures of the above cyclic alkylene hydrogen phosphites may also beutilized.

Some specific examples of suitable cyclic arylene hydrogen phosphitesare 2-oxo-(2H)-4,5-benzo-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-(3′-methylbenzo)-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-(4′-methylbenzo)-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-(4′-tert-butylbenzo)-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-naphthalo-1,3,2-dioxaphospholane, and the like. Mixturesof the above cyclic arylene hydrogen phosphites may also be utilized.

The iron-based catalyst composition utilized in this invention furthercomprises an organoaluminum compound, which has been designated asingredient (c). As used herein, the term “organoaluminum compound”refers to ny aluminum compound containing at least one aluminum-carbonbond. It is enerally advantageous to employ organoaluminum compoundsthat are soluble n a hydrocarbon solvent.

A preferred class of organoaluminum compounds that can be utilized isrepresented by the general formula AlR_(n)X_(3−n), where each R, whichmay be the same or different, is a mono-valent organic group that isattached to the aluminum atom via a carbon atom, where each X, which maybe the same or different, is a hydrogen atom, a carboxylate group, analkoxide group, or an aryloxide group, and where n is an integer of 1 to3. Preferably, each R is a hydrocarbyl group such as, but not limitedto, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl,substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl,alkaryl, and alkynyl groups, with each group preferably containing from1 carbon atom, or the appropriate minimum number of carbon atoms to formthe group, up to about 20 carbon atoms. These hydrocarbyl groups maycontain heteroatoms such as, but not limited to, nitrogen, oxygen,silicon, sulfur, and phosphorus atoms. Preferably, each X is acarboxylate group, an alkoxide group, or an aryloxide group, with eachgroup preferably containing from 1 carbon atom, or the appropriateminimum number of carbon atoms to form the group, up to about 20 carbonatoms.

Thus, some suitable types of organoaluminum compounds that can beutilized include, but are not limited to, trihydrocarbylaluminum,dihydrocarbylaluminum hydride, hydrocarbylaluminum dihydride,dihydrocarbylaluminum carboxylate, hydrocarbylaluminum bis(carboxylate),dihydrocarbylaluminum alkoxide, hydrocarbylaluminum dialkoxide,dihydrocarbylaluminum aryloxide, hydrocarbylaluminum diaryloxide, andthe like, and mixtures thereof. Trihydrocarbylaluminum compounds aregenerally preferred.

Some specific examples of organoaluminum compounds that can be utilizedinclude trimethylaluminum, triethylaluminum, triisobutylaluminum,tri-n-propylaluminum, triisopropylaluminum, tri-n-butylaluminum,tri-n-hexylaluminum, tri-n-octylaluminum, tricyclohexylaluminum,triphenylaluminum, tri-p-tolyl-aluminum, tribenzylaluminum,diethylphenylaluminum, diethyl-p-tolylaluminum, diethylbenzylaluminum,ethyldiphenylaluminum, ethyldi-p-tolylaluminum, ethyl-dibenzylaluminum,diethylaluminum hydride, di-n-propylaluminum hydride,diisopropylaluminum hydride, di-n-butylaluminum hydride,diisobutylaluminum hydride, di-n-octylaluminum hydride, diphenylaluminumhydride, di-p-tolyl-aluminum hydride, dibenzylaluminum hydride,phenylethylaluminum hydride, phenyl-n-propylaluminum hydride,phenylisopropylaluminum hydride, phenyl-n-butylaluminum hydride,phenylisobutylaluminum hydride, phenyl-n-octylaluminum hydride,p-tolylethylaluminum hydride, p-tolyl-n-propylaluminum hydride,p-tolylisopropylaluminum hydride, p-tolyl-n-butylaluminum hydride,p-tolyl-isobutylaluminum hydride, p-tolyl-n-octylaluminum hydride,benzylethylaluminum hydride, benzyl-n-propylaluminum hydride,benzylisopropylaluminum hydride, benzyl-n-butylaluminum hydride,benzylisobutylaluminum hydride, and benzyl-n-octylaluminum hydride,ethylaluminum dihydride, n-propylaluminum dihydride, isopropylaluminumdihydride, n-butylaluminum dihydride, isobutylaluminum dihydride,n-octylaluminum dihydride, dimethylaluminum hexanoate, diethylaluminumoctoate, diisobutylaluminum 2-ethylhexanoate, dimethylaluminumneodecanoate, diethyl-aluminum stearate, diisobutylaluminum oleate,methylaluminum bis(hexanoate), ethylaluminum bis(octoate),isobutylaluminum bis(2-ethylhexanoate), methyl-aluminumbis(neodecanoate), ethylaluminum bis(stearate), isobutylaluminumbis(oleate), dimethylaluminum methoxide, diethylaluminum methoxide,diisobutyl-aluminum methoxide, dimethylaluminum ethoxide,diethylaluminum ethoxide, diisobutylaluminum ethoxide, dimethylaluminumphenoxide, diethylaluminum phenoxide, diisobutylaluminum phenoxide,methylaluminum dimethoxide, ethylaluminum dimethoxide, isobutylaluminumdimethoxide, methylaluminum diethoxide, ethylaluminum diethoxide,isobutylaluminum diethoxide, methyl-aluminum diphenoxide, ethylaluminumdiphenoxide, isobutylaluminum diphenoxide, and the like, and mixturesthereof.

Another class of organoaluminum compounds that can be utilized isaluminoxanes. Aluminoxanes are well known in the art and compriseoligomeric linear aluminoxanes that can be represented by the generalformula:

and oligomeric cyclic aluminoxanes that can be represented by thegeneral formula:

where x is an integer of 1 to about 100, preferably about 10 to about50; y is an integer of 2 to about 100, preferably about 3 to about 20;and each R⁴, which may be the same or different, is a mono-valentorganic group that is attached to the aluminum atom via a carbon atom.Preferably, each R⁴ is a hydrocarbyl group such as, but not limited to,alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl,substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl,alkaryl, and alkynyl groups, with each group preferably containing from1 carbon atoms, or the appropriate minimum number of carbon atoms toform these groups, up to about 20 carbon atoms. These hydrocarbyl groupsmay contain heteroatoms such as, but not limited to, nitrogen, oxygen,silicon, sulfur, and phosphorus atoms. It should be noted that thenumber of moles of the aluminoxane as used in this application refers tothe number of moles of the aluminum atoms rather than the number ofmoles of the oligomeric aluminoxane molecules. This convention iscommonly employed in the art of catalysis utilizing aluminoxanes.

In general, aluminoxanes can be prepared by reactingtrihydrocarbylaluminum compounds with water. This reaction can beperformed according to known methods, such as (1) a method in which thetrihydrocarbylaluminum compound is dissolved in an organic solvent andthen contacted with water, (2) a method in which thetrihydrocarbylaluminum compound is reacted with water of crystallizationcontained in, for example, metal salts, or water adsorbed in inorganicor organic compounds, and (3) a method in which thetrihydrocarbylaluminum compound is added to the monomer or monomersolution that is to be oligomerized, and then water is added.

Some specific examples of aluminoxane compounds that can be utilizedinclude methylaluminoxane (MAO), modified methylaluminoxane (MMAO),ethylaluminoxane, butylaluminoxane, isobutylaluminoxane, and the like,and mixtures thereof. Isobutylaluminoxane is particularly useful on thegrounds of its availability and its solubility in aliphatic andcycloaliphatic hydrocarbon solvents. Modified methylaluminoxane can beformed by substituting about 20-80% of the methyl groups ofmethylaluminoxane with C₂ to C₁₂ hydrocarbyl groups, preferably withisobutyl groups, by using techniques known to those skilled in the art.

The iron-based catalyst composition utilized in this invention has avery high catalytic activity for polymerizing 1,3-butadiene intosyndiotactic 1,2-polybutadiene over a wide range of total catalystconcentrations and catalyst ingredient ratios. The polymers having themost desirable properties, however, are obtained within a narrower rangeof total catalyst concentrations and catalyst ingredient ratios.Further, it is believed that the three catalyst ingredients (a), (b),and (c) can interact to form an active catalyst species. Accordingly,the optimum concentration for any one catalyst ingredient is dependentupon the concentrations of the other catalyst ingredients. The molarratio of the hydrogen phosphite to the iron-containing compound (P/Fe)can be varied from about 0.5:1 to about 50:1, more preferably from about1:1 to about 25:1, and even more preferably from about 2:1 to about10:1. The molar ratio of the organoaluminum compound to theiron-containing compound (Al/Fe) can be varied from about 1:1 to about100:1, more preferably from about 3:1 to about 50:1, and even morepreferably from about 5:1 to about 25:1.

As discussed above, the iron-based catalyst composition utilized in thepresent invention is preferably formed by combining the three catalystingredients (a), (b), and (c). Although an active catalyst species isbelieved to result from this combination, the degree of interaction orreaction between the various ingredients or components is not known withany great degree of certainty. Therefore, it should be understood thatthe term “catalyst composition” has been employed to encompass a simplemixture of the ingredients, a complex of the various ingredients that iscaused by physical or chemical forces of attraction, a chemical reactionproduct of the ingredients, or a combination of the foregoing.

The iron-based catalyst composition utilized in this invention can beformed by combining or mixing the catalyst ingredients or components byusing, for example, one of the following methods.

First, the catalyst composition may be formed in situ by adding thethree catalyst ingredients to the rubber cement containing the rubberyelastomer and 1,3-butadiene monomer in either a stepwise or simultaneousmanner. When adding the catalyst ingredients in a stepwise manner, thesequence in which the ingredients are added is not critical. Preferably,however, the iron-containing compound is added first, followed by thehydrogen phosphite, and then followed by the organoaluminum compound.

Second, the three catalyst ingredients may be pre-mixed outside thepolymerization system at an appropriate temperature, which is generallyfrom about −20° C. to about 80° C., and the resulting catalystcomposition is then added to the rubber cement containing the rubberyelastomer and 1,3-butadiene monomer.

Third, the catalyst composition may be pre-formed in the presence of1,3-butadiene monomer. That is, the three catalyst ingredients arepre-mixed in the presence of a small amount of 1,3-butadiene monomer atan appropriate temperature, which is generally from about −20° C. toabout 80 ° C. The amount of 1,3-butadiene monomer that is used for thecatalyst pre-forming can range from about 1 to about 500 moles per moleof the iron-containing compound, and preferably should be from about 4to about 100 moles per mole of the iron-containing compound. Theresulting catalyst composition is then added to the rubber cementcontaining the rubbery elastomer and the remainder of the 1,3-butadienemonomer that is to be polymerized.

Fourth, as a further variation, the catalyst composition can also beformed by using a two-stage procedure. The first stage involvescombining the iron-containing compound and the organoaluminum compoundin the presence of a small amount of 1,3-butadiene monomer at anappropriate temperature, which is generally from about −20° C. to about80° C. In the second stage, the foregoing reaction mixture and thehydrogen phosphite are charged in either a stepwise or simultaneousmanner to the rubber cement containing the rubbery elastomer and theremainder of the 1,3-butadiene monomer that is to be polymerized.

Fifth, an alternative two-stage procedure may also be employed. Aniron-ligand complex is first formed by pre-combining the iron-containingcompound and the hydrogen phosphite compound. Once formed, thisiron-ligand complex is then combined with the organoaluminum compound toform the active catalyst species. The iron-ligand complex can be formedseparately or in the rubber cement containing the rubbery elastomer andthe 1,3-butadiene monomer that is to be polymerized. This complexationreaction can be conducted at any convenient temperature at normalpressure, but for an increased rate of reaction, it is preferred toperform this reaction at room temperature or above. The time requiredfor the formation of the iron-ligand complex is usually within the rangeof about 10 minutes to about 2 hours after mixing the iron-containingcompound with the hydrogen phosphite compound. The temperature and timeused for the formation of the iron-ligand complex will depend uponseveral variables including the particular starting materials and thesolvent employed. Once formed, the iron-ligand complex can be usedwithout isolation from the complexation reaction mixture. If desired,however, the iron-ligand complex may be isolated from the complexationreaction mixture before use.

Sixth, the three catalyst ingredients may be added to the rubber cementprior to or simultaneously with the addition of 1,3-butadiene monomer.

When a solution of the iron-based catalyst composition or one or more ofthe catalyst ingredients is prepared outside the polymerization systemas set forth in the foregoing methods, an organic solvent or carrier ispreferably employed. Useful solvents include hydrocarbon solvents suchas aromatic hydrocarbons, aliphatic hydrocarbons, and cycloaliphatichydrocarbons. Non-limiting examples of aromatic hydrocarbon solventsinclude benzene, toluene, xylenes, ethylbenzene, diethylbenzene,mesitylene, and the like. Non-limiting examples of aliphatic hydrocarbonsolvents include n-pentane, n-hexane, n-heptane, n-octane, n-nonane,n-decane, isopentane, isohexanes, isopentanes, isooctanes,2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirits, andthe like. And, non-limiting examples of cycloaliphatic hydrocarbonsolvents include cyclopentane, cyclohexane, methylcyclopentane,methylcyclohexane, and the like. Commercial mixtures of the abovehydrocarbons may also be used. For environmental reasons, aliphatic andcycloaliphatic solvents are highly preferred. The foregoing organicsolvents may serve to dissolve the catalyst composition or ingredients,or the solvent may simply serve as a carrier in which the catalystcomposition or ingredients may be suspended.

The production of blends of syndiotactic 1,2-polybutadiene and rubberyelastomers according to this invention is accomplished by polymerizing1,3-butadiene monomer within the rubber cement by using a catalyticallyeffective amount of the foregoing iron-based catalyst composition. Tounderstand what is meant by a catalytically effective amount, it shouldbe understood that the total catalyst concentration to be employed inthe polymerization mass depends on the interplay of various factors suchas the purity of the ingredients, the polymerization temperature, thepolymerization rate and conversion desired, and many other factors.Accordingly, a specific total catalyst concentration cannot bedefinitively set forth except to say that catalytically effectiveamounts of the respective catalyst ingredients should be used.Generally, the amount of the iron-containing compound used can be variedfrom about 0.01 to about 2 mmol per 100 g of 1,3-butadiene monomer, witha more preferred range being from about 0.02 to about 1.0 mmol per 100 gof 1,3-butadiene monomer, and a most preferred range being from about0.05 to about 0.5 mmol per 100 g of 1,3-butadiene monomer.

In performing the polymerization of 1,3-butadiene into syndiotactic1,2-polybutadiene within the rubber cement, a molecular weight regulatormay be employed to control the molecular weight of the syndiotactic1,2-polybutadiene to be produced. As a result, the scope of thepolymerization system can be expanded in such a manner that it can beused for the production of syndiotactic 1,2-polybutadiene having a widerange of molecular weights. Suitable types of molecular weightregulators that can be utilized include, but are not limited to,α-olefins such as ethylene, propylene, 1-but:ene, 1-pentene, 1-hexene,1-heptene, and 1-octene; accumulated diolefins such as allene and1,2-butadiene; nonconjugated diolefins such as 1,6-octadiene,5-methyl-1,4-hexadiene, 1,5-cyclooctadiene, 3,7-dimethyl-1,6-octadiene,1,4-cyclohexadiene, 4-vinylcyclohexene, 1,4-pentadiene, 1,4-hexadiene,1,5-hexadiene, 1,6-heptadiene, 1,2-divinylcyclohexane,5-ethylidene-2-norbornene, 5-methylene-2-norbornene,5-vinyl-2-norbornene, dicyclopentadiene, and 1,2,4-trivinylcyclohexane;acetylenes such as acetylene, methylacetylene and vinylacetylene; andmixtures thereof. The amount of the molecular weight regulator used,expressed in parts per hundred parts by weight of the 1,3-butadienemonomer (phm), is from about 0.01 to about 10 phm, preferably from about0.02 to about 2 phm, and more preferably from about 0.05 to about 1 phm.

The molecular weight of the syndiotactic 1,2-polybutadiene to beproduced can also be effectively controlled by conducting thepolymerization of 1,3-butadiene monomer in the presence of hydrogen gas.In this case, the partial pressure of hydrogen gas is preferably fromabout 0.01 to about 50 atmospheres.

The polymerization of 1,3-butadiene into syndiotactic 1,2-polybutadienewithin the rubber cement may be carried out as a batch process, acontinuous process, or even a semi-continuous process. In thesemi-continuous process, 1,3-butadiene monomer is intermittently chargedas needed to replace that monomer already polymerized. In any case, thepolymerization is desirably conducted under anaerobic conditions byusing an inert protective gas such as nitrogen, argon or helium, withmoderate to vigorous agitation. The polymerization temperature may varywidely from a low temperature, such as −10° C. or below, to a hightemperature such as 100° C. or above, with a preferred temperature rangebeing from about 20° C. to about 90° C. The heat of polymerization maybe removed by external cooling, cooling by evaporation of the1,3-butadiene monomer or the solvent, or a combination of the twomethods. Although the polymerization pressure employed may vary widely,a preferred pressure range is from about 1 atmosphere to about 10atmospheres.

Once a desired conversion is achieved, the polymerization of1,3-butadiene monomer into syndiotactic 1,2-polybutadiene within therubber cement can be stopped by adding a polymerization terminator thatinactivates the iron-based catalyst system. Typically, the terminatoremployed to inactivate the catalyst system is a protic compound, whichincludes, but is not limited to, an alcohol, a carboxylic acid, aninorganic acid, water, or a combination thereof. An antioxidant such as2,6-di-tert-butyl-4-methylphenol may be added along with, before orafter the addition of the terminator. The amount of the antioxidantemployed is usually in the range of 0.2% to 1% by weight of the polymerproduct. When the polymerization reaction has been stopped, the blend ofsyndiotactic 1,2-polybutadiene and the rubbery elastomer can berecovered from the polymerization mixture by utilizing conventionalprocedures of desolventization and drying. For instance, the blend ofsyndiotactic 1,2-polybutadiene and the rubbery elastomer may be isolatedfrom the polymerization mixture by coagulation of the polymerizationmixture with an alcohol such as methanol, ethanol, or isopropanol, or bysteam distillation of the solvent and the unreacted 1,3-butadienemonomer, followed by filtration. The product is then dried to removeresidual amounts of solvent and water. The polymer blend produced is ahighly dispersed blend of crystalline syndiotactic 1,2-polybutadiene inthe rubbery elastomer.

Advantageously, the iron-based catalyst composition employed in thisinvention can be manipulated to vary the characteristics of thesyndiotactic 1,2-polybutadiene in the polymer blend. Namely, thesyndiotactic 1,2-polybutadiene in the polymer blend made by the processof this invention can have various melting temperatures, molecularweights, 1,2-linkage contents, and syndiotacticities, all of which aredependent upon selection of the catalyst ingredients and the ingredientratios. For example, it has been found that the melting temperature,molecular weight, 1,2-linkage content, and syndiotacticity of thesyndiotactic 1,2-polybutadiene can be increased by using anorganoaluminum compound containing sterically bulky organic groups.Non-limiting examples of these sterically bulky organic groups includeisopropyl, isobutyl, t-butyl, cyclohexyl, and 2,6-dimethylphenyl groups.The use of acyclic hydrogen phosphites in lieu of cyclic hydrogenphosphites will also increase the melting temperature, molecular weight,1,2-linkage content, and syndiotacticity of the syndiotactic1,2-polybutadiene. Manipulation of the characteristics of thesyndiotactic 1,2-polybutadiene by varying catalyst ingredients andratios is described in greater detail in co-pending applications U.S.Ser. Nos. 09/172,305, 09/173,956, and 09/439,861.

The blends of syndiotactic 1,2-polybutadiene and rubbery elastomersproduced with the process of this invention have many uses. For example,these blends can be utilized in rubber compositions that are used tomanufacture the supporting carcass, innerliner, and tread of tires. Theblends of syndiotactic 1,2-polybutadiene and rubbery elastomers are alsouseful in the manufacture of films and packaging materials and in manymolding applications.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested as described in theExamples disclosed hereinbelow. The examples should not, however, beconstrued as limiting the scope of the invention. The claims will serveto define the invention.

EXAMPLES Example 1

In this experiment, a highly dispersed blend of syndiotactic1,2-polybutadiene and low-vinyl polybutadiene was prepared bypolymerizing 1,3-butadiene monomer into syndiotactic 1,2-polybutadienewithin a low-vinyl polybutadiene rubber cement.

The low-vinyl polybutadiene rubber cement was prepared by charging 449 gof hexanes, 911 g of a 1,3-butadiene/hexanes blend containing 22.4% byweight of 1,3-butadiene, and 0.64 mL of 1.60 M n-butyllithium in hexanesto a two-gallon stainless-steel reactor. The polymerization was carriedout at 65° C. for 6 hours. The catalyst was inactivated by the additionof 1.02 mL of 1.0 M diethylaluminum chloride. The conversion of the1,3-butadiene monomer to low-vinyl polybutadiene was determined to beessentially 100% by measuring the weight of the polymer recovered from asmall portion of the rubber cement.

After the low-vinyl polybutadiene rubber cement produced above wascooled to room temperature, 1048 g of hexanes and 2126 g of a1,3-butadiene/hexanes blend containing 22.4% by weight of 1,3-butadienewere added to the rubber cement. The polymerization of the 1,3-butadienemonomer into syndiotactic 1,2-polybutadiene was initiated by theaddition of 20.0 mL of 0.0595 M iron(III) 2-ethylhexanoate in hexanes,17.9 mL of 0.266 M bis(2-ethylhexyl) hydrogen phosphite in hexanes, and28.0 mL of 0.68 M of triisobutylaluminum in hexanes. The polymerizationwas conducted at 65° C. for 4 hours. The polymerization was stopped bythe addition of 3 mL of isopropanol diluted with 50 mL of hexanes. Thepolymerization mixture was added to 10 liters of isopropanol containing12 g of 2,6-di-tert-butyl-4-methylphenol. The resulting blend ofsyndiotactic 1,2-polybutadiene and low-vinyl polybutadiene was isolatedby filtration and dried to a constant weight under vacuum at 60° C. Theyield of the polymer blend was 647 g. The conversion of the1,3-butadiene monomer to the syndiotactic 1,2-polybutadiene wascalculated to be 93%. As determined by differential scanning calorimetry(DSC), the polymer blend had a glass transition temperature of −93° C.resulting from the low-vinyl polybutadiene and a melting temperature of183° C. resulting from the syndiotactic 1,2-polybutadiene.

Example 2

In this experiment, the procedure of Example 1 was repeated, except thatthe polymerization of the 1,3-butadiene monomer into syndiotactic1,2-polybutadiene within the low-vinyl polybutadiene rubber cement wasinitiated by the addition of 32.0 mL of 0.0595 M iron(III)2-ethylhexanoate in hexanes, 39.5 mL of 0.193 M2-oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane in cyclohexane, and39.2 mL of 0.68 M of triisobutylaluminum in hexanes. After work-up ofthe polymerization mixture, a highly dispersed blend of syndiotactic1,2-polybutadiene and low-vinyl polybutadiene was obtained. The yield ofthe polymer blend was 623 g. The conversion of the 1,3-butadiene monomerto the syndiotactic 1,2-polybutadiene was calculated to be 88%. Asdetermined by differential scanning calorimetry (DSC), the polymer blendhad a glass transition temperature of −93° C. resulting from thelow-vinyl polybutadiene, and a melting temperature of 155° C. resultingfrom the syndiotactic 1,2-polybutadiene.

Example 3

In this experiment, a highly dispersed blend of syndiotactic1,2-polybutadiene and high cis-1,4-polybutadiene was prepared bypolymerizing 1,3-butadiene monomer into syndiotactic 1,2-polybutadienewithin a high cis-1,4-polybutadiene rubber cement.

The high cis-1,4-polybutadiene rubber cement was prepared by charging449 g of hexanes, 911 g of a 1,3-butadiene/hexanes blend containing22.4% by eight of 1,3-butadiene, 9.0 mL of 0.68 M triisobutylaluminum inhexanes, 0.41 mL of 1.0 M diethylaluminum chloride, and 0.39 mL of 0.520M neodymium(III) neodecanoate in cyclohexane to a two-gallonstainless-steel reactor. The polymerization was carried out at 80° C.for 5 hours. The conversion of the 1,3-butadiene monomer to highcis-1,4-polybutadiene was determined to be 96% by measuring the weightof the polymer recovered from a small portion of the rubber cement.

After the high cis-1,4-polybutadiene rubber cement produced above wascooled to room temperature, 1048 g of hexanes and 2126 g of a1,3-butadiene/hexanes blend containing 22.4%byweightof 1,3-butadienewere added to the rubber cement. The polymerization of the 1,3-butadienemonomer into syndiotactic 1,2-polybutadiene was initiated by theaddition of 16.0 mL of 0.0595 M iron(III) 2-ethylhexanoate in hexanes,14.3 mL of 0.266 M bis(2-ethylhexyl) hydrogen phosphite in hexanes, and21.0 mL of 0.68 M of triisobutylaluminum in hexanes. The polymerizationwas conducted at 65° C. for 4 hours. The polymerization was stopped bythe addition of 3 mL of isopropanol diluted with 50 mL of hexanes. Thepolymerization mixture was added to 10 liters of isopropanol containing12 g of 2,6-di-tert-butyl-4-methylphenol. The resulting blend ofsyndiotactic 1,2-polybutadiene and high cis-1,4-polybutadiene wasisolated by filtration and dried to a constant weight under vacuum at60° C. The yield of the polymer blend was 651 g. The conversion of the1,3-butadiene monomer to the syndiotactic 1,2-polybutadiene wascalculated to be 94%. As determined by differential scanning calorimetry(DSC), the polymer blend had a glass transition temperature of −103° C.and a melting temperature of −8° C. resulting from the highcis-1,4-polybutadiene, and a melting temperature of 184° C. resultingfrom the syndiotactic 1,2-polybutadiene.

Example 4

In this experiment, the procedure of Example 3 was repeated except thatthe polymerization of the 1,3-butadiene monomer into syndiotactic1,2-polybutadiene within the high cis-1,4-polybutadiene rubber cementwas initiated by the addition of 32.0 mL of 0.0595 M iron(III)2-ethylhexanoate in hexanes, 39.5 mL of 0.193 M2-oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane in cyclohexane, and39.2 mL of 0.68 M of triisobutylaluminum in hexanes. After work-up ofthe polymerization mixture, a highly dispersed blend of syndiot:actic1,2-polybutadiene and high cis-1,4-polybutadiene was obtained. The yieldof the polymer blend was 637 g. The conversion of the 1,3-butadienemonomer to the syndiotactic 1,2-polybutadiene was calculated to be 91%.As determined by differential scanning calorimetry (DSC), the polymerblend had a glass transition temperature of −104° C. and a meltingtemperature of −7° C. resulting from the high cis-1,4-polybutadiene, anda melting temperature of 157° C. resulting from the syndiotactic1,2-polybutadiene.

In Examples 1-4, after the polymer blend cement was removed from thereactor, visual inspection of the interior of the reactor revealed thatthe reactor was relatively clean with minimal fouling.

Comparative Example 5

In this experiment, the polymerization of 1,3-butadiene monomer intosyndiotactic 1,2-polybutadiene was conducted in the absence of a rubbercement. In the procedure used, a two-gallon stainless-steel reactor wascharged with 2408 g of hexanes, 2126 g of a 1,3-butadiene/hexanes blendcontaining 22.4% by weight of 1,3-butadiene, 16.0 mL of 0.0595 Miron(III) 2-ethylhexanoate in hexanes, 14.3 mL of 0.266 Mbis(2-ethylhexyl) hydrogen phosphite in hexanes, and 21.0 mL of 0.68 Mof triisobutylaluminum in hexanes. The polymerization was conducted at65° C. for 4 hours. The polymerization was stopped by the addition of 3mL of isopropanol diluted with 50 mL of hexanes. The polymerizationmixture was removed from the reactor and added to 10 liters ofisopropanol containing 12 g of 2,6-di-tert-butyl-4-methylphenol. Visualinspection of the interior of the reactor revealed that severe reactorfouling had occurred. In particular, the blades and shafts of theagitator were covered with chunks of agglomerated polymer particles, andthe reactor wall was coated with a thick polymer film. Due to reactorfouling, the reactor had to be opened to recover the remaining polymerinside the reactor. The total yield of the syndiotactic1,2-polybutadiene that was recovered was 457 g (96%). As determined bydifferential scanning calorimetry (DSC), the polymer had a meltingtemperature of 186° C.

This comparative experiment showed that reactor fouling can be a seriousproblem in the synthesis of syndiotactic 1,2-polybutadiene in theabsence of a rubber cement. Examples 1-4 show that by utilizing theprocess of the present invention, the problem of reactor foulingassociated with the synthesis of syndiotactic 1,2-polybutadiene can begreatly reduced.

Although the present invention has been described in the above exampleswith reference to particular means, materials and embodiments, it wouldbe obvious to persons skilled in the art that various changes andmodifications may be made, which fall within the scope claimed for theinvention as set out in the appended claims. The invention is thereforenot limited to the particulars disclosed and extends to all equivalentswithin the scope of the claims.

What is claimed is:
 1. A process for preparing blends of syndiotactic1,2-polybutadiene and rubbery elastomers comprising the steps of: (1)providing a mixture of a rubber cement and 1,3-butadiene monomer; and(2) polymerizing the 1,3-butadiene monomer into syndiotactic1,2-polybutadiene within the rubber cement by using a catalystcomposition that is the combination of or the reaction product ofingredients comprising: (a) an iron-containing compound; (b) a hydrogenphosphite; and (c) an organoaluminum compound.
 2. The process of claim1, where said step of providing the mixture of a rubber cement and1,3-butadiene monomer comprises the step of preparing a rubber cement bypolymerizing one or more monomers in an organic solvent to form rubberyelastomers, and then the step of adding 1,3-butadiene monomer to therubber cement.
 3. The process of claim 1, where said step of providingthe mixture of a rubber cement and 1,3-butadiene monomer comprises thestep of dissolving one or more preformed rubbery elastomers in anorganic solvent, and then the step of adding of 1,3-butadiene monomer.4. The process of claim 1, where the rubbery elastomers are naturalrubber, cis-1,4-polybutadiene, amorphous 1,2-poly-butadiene,polyisoprene, polyisobutylene, neoprene, ethylene-propylene copolymerrubber, styrene-butadiene rubber, styrene-isoprene rubber,styrene-isoprene-butadiene rubber, styrene-butadiene-styrene blockcopolymer, styrene-butadiene block copolymer, hydrogenatedstyrene-butadiene-styrene block copolymer, hydrogenatedstyrene-butadiene block copolymer, styrene-isoprene-styrene blockcopolymer, styrene-isoprene block copolymer, hydrogenatedstyrene-isoprene-styrene block copolymer, hydrogenated styrene-isopreneblock copolymer, polysulfide rubber, acrylic rubber, urethane rubber,silicone rubber, epichlorohydrin rubber, or mixtures thereof.
 5. Theprocess of claim 2, where the organic solvent is n-pentane, n-hexane,n-heptane, n-octane, n-nonane, n-decane, isopentane, isohexanes,isoheptanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene,petroleum spirits, cyclopentane, cyclohexane, methylcyclopentane,methylcyclohexane, benzene, toluene, xylenes, ethylbenzene,diethylbenzene, mesitylene, or a mixture thereof.
 6. The process ofclaim 3, where the organic solvent is n-pentane, n-hexane, n-heptane,n-octane, n-nonane, n-decane, isopentane, isohexanes, isoheptanes,isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, petroleumspirits, cyclopentane, cyclohexane, methylcyclopentane,methylcyclohexane, benzene, toluene, xylenes, ethylbenzene,diethylbenzene, mesitylene, or a mixture thereof.
 7. The process ofclaim 1, where the concentration of the rubbery elastomers within therubber cement is from about 5% to about 35% by weight of the rubbercement.
 8. The process of claim 1, where said step of polymerizing1,3-butadiene monomer into syndiotactic 1,2-polybutadiene is conductedin the presence of about 0.01 to about 2 mmol of the iron-containingcompound per 100 g of 1,3-butadiene.
 9. The process of claim 1, wherethe iron atom in the iron-containing compound has an oxidation state of0, +2, +3, or +4.
 10. The process of claim 1, where the iron-containingcompound is an iron carboxylate, iron carbamate, iron dithiocarbamate,iron xanthate, iron β-diketonate, iron alkoxide, iron aryloxide,organoiron compound, or a mixture thereof.
 11. The process of claim 1,where the hydrogen phosphite is an acyclic hydrogen phosphite defined bythe following keto-enol tautomeric structures:

or a cyclic hydrogen phosphite defined by the following keto-enoltautomeric structures:

or a mixture thereof, where R¹ and R², which may be the same ordifferent, are mono-valent organic groups, and where R³ is a divalentorganic group.
 12. The process of claim 11, where R¹ and R² are alkyl,cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substitutedcycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, oralkynyl groups, with each group containing up to about 20 carbon atoms,and where R³ is an alkylene, cycloalkylene, substituted alkylene,substituted cycloalkylene, alkenylene, cycloalkenylene, substitutedalkenylene, substituted cycloalkenylene, arylene, or substituted arylenegroup, with each group containing up to about 20 carbon atoms.
 13. Theprocess of claim 1, where the organoaluminum compound is defined by theformula AlR_(n)X_(3−n), where each R, which may be the same ordifferent, is a mono-valent organic group, where each X, which may bethe same or different, is a hydrogen atom, a carboxylate group, analkoxide group, or an aryloxide group, and where n is an integerincluding 1, 2 or
 3. 14. The process of claim 13, where each R is analkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl,substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl,alkaryl, or alkynyl group, with each group containing up to about 20carbon atoms, and where each X is a carboxylate group, an alkoxidegroup, or an aryloxide group, with each group containing up to about 20carbon atoms.
 15. The process of claim 1, where the organoaluminumcompound is trihydrocarbylaluminum, dihydrocarbylaluminum hydride,hydrocarbylaluminum dihydride, dihydrocarbylaluminum carboxylate,hydrocarbylaluminum bis(carboxylate), dihydrocarbylaluminum alkoxide,hydrocarbylaluminum dialkoxide, dihydrocarbylaluminum aryloxide,hydrocarbylaluminum diaryloxide, or a mixture thereof.
 16. The processof claim 1, where the organoaluminum compound is an aluminoxane definedby one of the following formulas:

where x is an integer of 1 to about 100, y is an integer of 2 to about100, and each R⁴, which may be the same or different, is a mono-valentorganic group.
 17. The process of claim 16, where each R⁴ is an alkyl,cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substitutedcycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, oralkynyl group, with each group containing up to about 20 carbon atoms.18. The process of claim 1, where the molar ratio of the hydrogenphosphite to the iron-containing compound is from about 0.5:1 to about50:1, and the molar ratio of the organoaluminum compound to theiron-containing compound is from about 1:1 to about 100:1.
 19. Aprocessfor producing blends of syndiotactic 1,2-polybutadiene and rubberyelastomers comprising the steps of: (1) providing a mixture of a rubbercement and 1,3-butadiene monomer; and (2) polymerizing the 1,3-butadienemonomer into syndiotactic 1,2-polybutadiene within the rubber cement byusing a catalyst composition that is formed by combining: (a) aniron-containing compound; (b) a hydrogen phosphite; and (c) anorganoaluminum compound.
 20. The process of claim 1, where the molarratio of the hydrogen phosphite to the iron-containing compound is fromabout 1:1 to about 25:1, and the molar ratio of the organoaluminumcompound to the iron-containing compound is from about 5:1 to about25:1.